1. Field of the Invention
The present invention relates to a dielectric barrier excimer lamp and an ultraviolet light beam irradiating apparatus to which the dielectric barrier excimer lamp is applied. More specifically, the present invention relates to a dielectric barrier excimer lamp for cleaning or modifying the surface of a semiconductor wafer or a glass substrate by means of joint activities of ultraviolet light beam and ozone, and an ultraviolet light beam irradiating apparatus having the dielectric barrier excimer lamp.
2. Related Art Statement
In recent years, studies are being widely made with regard to a method for cleaning or modifying a work such as a metal, a semiconductor substance or a glass by means of the joint activities of ultraviolet light beam and ozone. The above method is generally known as a UV ozone method. The UV ozone method has advantages that an organic contaminant adhering to a work surface can be removed, and that an oxide film can be formed on the surface, without damaging the work.
In the UV ozone method, air containing oxygen or oxygen gas is irradiated with 185 nm light that is a vacuum ultraviolet light beam radiated from a low-pressure mercury lamp, whereby ozone is generated. Active oxygen species that is a decomposed gas from ozone is generated from the ozone and brought into contact with a work surface. In cleaning the work by the UV ozone method, an organic contaminant adhering to the work surface is oxidized upon contact with the active oxygen species and converted to low-molecular oxides such as carbon dioxide and water, whereby it is removed from the surface. In this manner, the work surface can be finely dry-cleaned.
A low-pressure mercury lamp has greatly contributed to wide use of the above UV ozone cleaning due to its characteristic emitted light beam, and in recent years, a dielectric barrier excimer lamp has come to be known as a light source capable of providing more efficient cleaning and is replacing the conventional low-pressure mercury lamp as a light source for the UV ozone cleaning. The dielectric barrier excimer lamp has advantages that it overcomes the problems of heat radiation to a substrate, lighting performance, etc., which have been defects of the low-pressure mercury lamp, further that it has an emitted light beam having a shorter wavelength so that it is excellent in breaking an organic compound and that it can more efficiently generate active oxygen.
FIG. 13 shows one constitution of a conventional dielectric barrier excimer lamp unit. As shown in FIG. 13, a lamp unit 40 has an excimer lamp 42 inside a metal container 41. The excimer lamp 42 has an inner cylindrical tube 42a and an outer cylindrical tube 42b both made of quartz glass and has a discharge gas 43 such as xenon gas charged in a space between these tubes. And, a high voltage is applied between electrodes 42c and 42d provided inside and outside the tubes (the electrode on the outside thereof has the form of a network) from an alternate current power source (not shown), whereby the excimer lamp 42 radiates ultraviolet light. That is, upon application of the high voltage, the quartz glass that is a dielectric material generates a microdischarge due to dielectric barrier discharge (silent discharge), to excite and combine the discharge gas 43 charged inside with the energy of the microdischarge, and the gas molecules in an excited state radiate light beam having a wavelength characteristic of the gas in the process of the gas molecules restoring their ground state.
The metal container 41 of the lamp unit 40 has a light window 44 made of a synthetic quartz glass, and an ultraviolet light beam radiated from the excimer lamp 42 is transmitted through it and a work is irradiated therewith. In the metal container 41, an inert gas such as nitrogen gas is constantly flowed at a rate of several liters per minute, so that the attenuation of the ultraviolet light beam from the excimer lamp 42 controlled to make it as small as possible. Further, the metal container 41 internally has a reflection plate 45 (or the inner wall surface of the metal container is mirror-processed), whereby an ultraviolet light beam radiated upward and sideward from the excimer lamp 42 is reflected thereon and led toward the light window 44. The ultraviolet light beam which comes out of the container through the light window 44 generates ozone and active oxygen species due to its photochemical reaction in an oxygen-containing atmosphere where a work is placed, to bring them into contact with the surface of the work, and further, the work is irradiated directly with this vacuum ultraviolet light beam, so that the cleaning and modification of the work is attained by co-working of these.
However, the above conventional dielectric barrier excimer lamp unit has the following problems.
(1) Ultraviolet light beam radiated upward and sideward from excimer lamp 42 is reflected on the reflection plate 45 and lead toward the light window 44. However, the reaching efficiency thereof is very low, and most of the above ultraviolet light beam radiated upward comes to nothing. The radiation efficiency of ultraviolet light beam based on power inputted to the excimer lamp 42 is very poor.
(2) The synthetic quartz used as a material for the above light window 44 is expensive and increases the cost of the unit. Particularly in a unit in which a plurality of the excimer lamps 42 are provided in the metal container 41 for broadening the irradiation region of the ultraviolet light beam, the light window 44 has a large area, which causes a serious cost problem.
(3) The above light window 44 made of the synthetic quartz causes so-called solarization which is a phenomenon that a color center is generated with slight impurities such as iron and manganese due to irradiation with ultraviolet light beam and blackening takes place. The transmitted-light quantity is attenuated due to the solarization, and as a result, the cleaning effect decreases.
(4) The inert gas such as nitrogen that is flowed into the metal container 41 is effective for decreasing absorption of ultraviolet light beam in the container. On the other hand, it requires an additional cost, and handling thereof requires labors in view of environmental protection.
(5) The outer electrode 42d is exposed on the outer circumference of the excimer lamp 42, so that it is required to take care when the excimer lamp 42 is attached inside the metal container 41. For this reason, the position of the excimer lamp 42 relative to the container is liable to vary when the excimer lamp 42 is attached, and the variability may influence the irradiation performance of the unit.
(6) The above metal container 41 has a relatively large space around the excimer lamp 42 for disposing the above reflection plate and attaching the excimer lamp 42. It is therefore required to constantly flow the inert gas necessary for filling the space with it at a rate of approximately several liters per minute, so that the consumption thereof comes to be very large.
(7) For improving the efficiency of cleaning or modifying the work with ultraviolet light beam, preferably, the distance between the surface of the excimer lamp 42 and the work is shortened so as to make it as small as possible, and the ultraviolet light beam is increased in radiation light quantity. In the conventional lamp unit, however, it is difficult to shorten the above distance due to its structure in which the excimer lamp is housed in the metal container.
Under the circumstances, it is a first object of the present invention to provide a dielectric barrier excimer lamp which can be improved in ultraviolet light beam radiation efficiency relative to power inputted to the excimer lamp and ultraviolet light beam irradiation efficiency to a work, which is easy to handle and less expensive and which attains the performance of a low running cost.
It is a second object of the present invention to provide an ultraviolet light beam irradiating apparatus with a dielectric barrier excimer lamp having the above excellent characteristics.
For achieving the above objects, the present inventors have made diligent studies and have found that the above objects can be achieved by a specifically structured dielectric barrier excimer lamp having at least a dielectric dual tube made of an inner tube, a light-transmitting outer tube and a discharge gas sealed in a space between these tubes and a pair of electrodes. The present invention has been accordingly completed on the basis of the above finding.
That is, the first object of the present invention can be achieved by
(1) a dielectric barrier excimer lamp comprising
a dielectric dual tube having an inner tube, a light-transmitting outer tube and a discharge gas sealed in a space between the inner and outer tubes,
a case for housing said dual tube, the case being opened at least on one side of said dual tube in radius direction of said dual tube,
an outer electrode which is fixed in an opened region of said case and includes a network-shaped region disposed close to the external-surface side of said outer tube on one side of said dual tube, and
an inner electrode disposed on an inner-surface side of said inner tube which inner-surface side corresponds at least to the region of the surface of said outer tube which surface is the surface close to which said outer electrode is disposed,
wherein a voltage is applied between said outer electrode and said inner electrode to radiate ultraviolet light beam through said network-shaped outer electrode (to be referred to as xe2x80x9cthe dielectric barrier excimer lamp Ixe2x80x9d of the present invention), and
(2) a dielectric barrier exciner lamp comprising
a dielectric dual tube having an inner tube, a light-transmitting outer tube and a discharge gas sealed in a space between the inner and outer tubes,
a network-shaped first electrode disposed close to the outer circumferential surface of said outer tube,
a second electrode disposed close to the inner circumferential surface of said inner tube, and
a light-transmitting dielectric first tube for internally housing said dual tube together with said first and second electrodes, an inert gas being introducible into a first space between said first tube and said outer tube,
wherein a voltage is applied between said first and second electrodes to radiate ultraviolet light beam (to be referred to as xe2x80x9cthe dielectric barrier excimer lamp IIxe2x80x9d of the present invention).
Further, the second object of the present invention can be achieved by an ultraviolet light beam irradiating apparatus with the above dielectric barrier excimer lamp I or II.